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Molecules 2017, 22(6), 866; doi:10.3390/molecules22060866

Encapsulation of the Antioxidant R-(+)-α-Lipoic Acid in Permethylated α- and β-Cyclodextrins: Thermal and X-ray Structural Characterization of the 1:1 Inclusion Complexes

Centre for Supramolecular Chemistry Research, Department of Chemistry, University of Cape Town, Rondebosch 7701, South Africa
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Academic Editor: Bernard Martel
Received: 9 January 2017 / Revised: 16 May 2017 / Accepted: 16 May 2017 / Published: 23 May 2017
(This article belongs to the Special Issue Cyclodextrin Chemistry)
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Abstract

The naturally occurring compound α-lipoic acid (ALA) is implicated in manifold critical biological roles and its potent antioxidant properties and potential for treatment of various diseases have led to its widespread use as a dietary supplement. However, shortcomings of poor aqueous solubility and low thermal stability have hampered its development as a medicinal agent, prompting the use of cyclodextrins (CDs) to address these problems. The paucity of published structural data on the nature of the interactions between ALA and CDs motivated the present study, which describes the synthesis and X-ray structural elucidation of crystalline inclusion complexes between the biologically relevant R-(+)-α-lipoic acid (RALA) and the host molecules permethylated α-CD (TMA) and permethylated β-CD (TMB). Single crystal X-ray diffraction of TMA·RALA·6H2O and TMB·RALA revealed significantly different orientations of the RALA molecule within the TMA and TMB cavities, but in both cases the guest molecule is fully encapsulated by the respective parent host molecules and residues of CD molecules of neighboring complex units. While pure RALA melted at 46–48 °C, combined thermal analysis techniques indicated that on heating the respective complexes, the release of RALA occurred at significantly higher onset temperatures, in the range 150–170 °C. View Full-Text
Keywords: R-(+)-α-lipoic acid; antioxidant; cyclodextrins; thermal analysis; X-ray diffraction; crystal structure; stability R-(+)-α-lipoic acid; antioxidant; cyclodextrins; thermal analysis; X-ray diffraction; crystal structure; stability
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Caira, M.R.; Bourne, S.A.; Mzondo, B. Encapsulation of the Antioxidant R-(+)-α-Lipoic Acid in Permethylated α- and β-Cyclodextrins: Thermal and X-ray Structural Characterization of the 1:1 Inclusion Complexes. Molecules 2017, 22, 866.

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